The majority of injuries and fatalities in road traffic related incidents occur to pedestrians. Although traffic regulation and education of pedestrians can achieves some reduction in the number of injuries and fatalities, in more recent years the focus has turned towards vehicle design in order to reduce the likelihood of injury to pedestrians in the event of a collision.
One area of development has been in ‘passive’ measures involving softening the points of a vehicle that a pedestrian would most likely impact during a collision. Known measures include redesigning bumpers (fenders), bonnets (hoods), windscreens and A-pillars to be more compliant during a collision without compromising the structural integrity of the vehicle, and the passenger cell particularly.
In addition to passive measures, so called ‘active’ systems have been developed which are able to manage the energy transfer during a collision more effectively. Such active systems include ‘pop-up’ bonnets in which an actuator deploys an entire bonnet upwardly in a collision. Here, the relatively compliant structure of the bonnet, usually being sheet metal, acts as a cushioning surface for the pedestrian and the raised position of the bonnet provides increased clearance from the engine bay to guard against the pedestrian impacting the harder components in it, such as the engine and suspension parts. A system like this goes some way to improving energy transfer management, although the considerable mass of the bonnet can act as a limitation on deployment speed; generally it is desirable to deploy the bonnet as quickly as possible so the mass of the bonnet compromises the deployment speed.
Other active systems are known. In one example, it is known to incorporate an airbag device in the cowl of the vehicle which deploys from under the bonnet in the event of a collision with a pedestrian. The bonnet also deploys upwardly a short way in this system. The airbag unit in such a device assumes a generally U-shaped configuration when it is fully inflated so the lateral base of the inflated airbag overlies the lower edge of the windscreen whilst the arms of the inflated airbag extend some way up the A-pillars at the sides of the windscreen thereby providing a cushioning surface on these vehicle hardpoints. Although such a system can provide a degree of protection for the pedestrian during impacts with the rear of the bonnet, the windscreen base and the A-pillars, its effectiveness is compromised by the limited space available to store such an airbag device having the necessary volume in the cowl of the vehicle, which is usually in use to store existing components such as air conditioning intakes, and windscreen wiper components. Furthermore, the entire mass of the bonnet must also be deployed which increases the energy consumption of the system and also limits deployment time.
It is against this background that the invention has been devised. Embodiments of the invention may provide an improved airbag device for a vehicle. Other aims and advantages of the invention will become apparent from the following description, claims and drawings.